Class Rewriter

Extension methods for IRewriter<T> implementations.

Inheritance
Object
Rewriter
Inherited Members
Namespace: Sawmill
Assembly: Sawmill.dll
Syntax
public static class Rewriter

Methods

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ChildrenInContext<T>(IRewriter<T>, T)

Returns an array containing each immediate child of value paired with a function to replace the child. This is typically useful when you need to replace a node's children one at a time, such as during mutation testing.

The replacement function can be seen as the "context" of the child; calling the function with a new child "plugs the hole" in the context.

SelfAndDescendantsInContext<T>(IRewriter<T>, T) DescendantsAndSelfInContext<T>(IRewriter<T>, T)
Declaration
public static (T item, Func<T, T> replace)[] ChildrenInContext<T>(this IRewriter<T> rewriter, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
T value

The value to get the contexts for the immediate children
Returns
Type Description
ValueTuple<T, Func<T, T>>[]
Type Parameters
Name Description
T
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Cursor<T>(IRewriter<T>, T)

Create a Cursor<T>(IRewriter<T>, T) focused on the root node of value.

Declaration
public static Cursor<T> Cursor<T>(this IRewriter<T> rewriter, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
T value

The root node on which the newly created Cursor<T>(IRewriter<T>, T) should be focused
Returns
Type Description
Cursor<T>

A Cursor<T>(IRewriter<T>, T) focused on the root node of value
Type Parameters
Name Description
T
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DescendantAt<T>(IRewriter<T>, IEnumerable<Direction>, T)

Returns the descendant at a particular location in value

Declaration
public static T DescendantAt<T>(this IRewriter<T> rewriter, IEnumerable<Direction> path, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
IEnumerable<Direction> path

The route to take to find the descendant
T value

The rewritable tree type
Returns
Type Description
T

The descendant found by following the directions in path
Type Parameters
Name Description
T
Exceptions
Type Condition
InvalidOperationException

Thrown if path leads off the edge of the tree
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DescendantsAndSelf<T>(IRewriter<T>, T)

Yields all of the nodes in the tree represented by value, starting at the bottom. SelfAndDescendants<T>(IRewriter<T>, T)

Declaration
public static IEnumerable<T> DescendantsAndSelf<T>(this IRewriter<T> rewriter, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
T value

The value to traverse
Returns
Type Description
IEnumerable<T>

An enumerable containing all of the nodes in the tree represented by value, starting at the bottom.
Type Parameters
Name Description
T

The rewritable tree type
Examples
Expr expr = new Add(
    new Add(
        new Lit(1),
        new Lit(2)
    ),
    new Lit(3)
);
Expr[] expected = new[]
    {
        new Lit(1),
        new Lit(2),
        new Add(new Lit(1), new Lit(2)),
        new Lit(3),
        expr    
    };
Assert.Equal(expected, rewriter.DescendantsAndSelf(expr));
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DescendantsAndSelfInContext<T>(IRewriter<T>, T)

Yields each node in the tree represented by value paired with a function to replace the node, starting at the bottom. This is typically useful when you need to replace nodes one at a time, such as during mutation testing.

The replacement function can be seen as the "context" of the node; calling the function with a new node "plugs the hole" in the context.

DescendantsAndSelf<T>(IRewriter<T>, T) ChildrenInContext<T>(IRewriter<T>, T) SelfAndDescendantsInContext<T>(IRewriter<T>, T)
Declaration
public static IEnumerable<(T item, Func<T, T> replace)> DescendantsAndSelfInContext<T>(this IRewriter<T> rewriter, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
T value

The value to get the contexts for the descendants
Returns
Type Description
IEnumerable<ValueTuple<T, Func<T, T>>>
Type Parameters
Name Description
T
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Fold<T, U>(IRewriter<T>, SpanFunc<U, T, U>, T)

Flattens all the nodes in the tree represented by value into a single result, using an aggregation function to combine each node with the results of folding its children.

Declaration
public static U Fold<T, U>(this IRewriter<T> rewriter, SpanFunc<U, T, U> func, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
SpanFunc<U, T, U> func

The aggregation function
T value

The value to fold
Returns
Type Description
U

The result of aggregating the tree represented by value.
Type Parameters
Name Description
T

The rewritable tree type
U

The type of the result of aggregation
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GetChildren<T>(IRewriter<T>, T)

Get the immediate children of the value. GetChildren(Span<T>)

Declaration
public static T[] GetChildren<T>(this IRewriter<T> rewriter, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
T value

The value
Returns
Type Description
T[]

The immediate children of value
Type Parameters
Name Description
T

The rewritable tree type
Examples

Given a representation of the expression (1+2)+3,

Expr expr = new Add(
    new Add(
        new Lit(1),
        new Lit(2)
    ),
    new Lit(3)
);

GetChildren<T>(IRewriter<T>, T) returns the immediate children of the topmost node.

Expr[] expected = new[]
    {
        new Add(
            new Lit(1),
            new Lit(2)
        ),
        new Lit(3)
    };
Assert.Equal(expected, rewriter.GetChildren(expr));
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ReplaceDescendantAt<T>(IRewriter<T>, IEnumerable<Direction>, T, T)

Replaces the descendant at a particular location in value

Declaration
public static T ReplaceDescendantAt<T>(this IRewriter<T> rewriter, IEnumerable<Direction> path, T newDescendant, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
IEnumerable<Direction> path

The route to take to find the descendant
T newDescendant

The replacement descendant
T value

The rewritable tree type
Returns
Type Description
T

A copy of value with newDescendant placed at the location indicated by path
Type Parameters
Name Description
T
Exceptions
Type Condition
InvalidOperationException

Thrown if path leads off the edge of the tree
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Rewrite<T>(IRewriter<T>, Func<T, T>, T)

Rebuild a tree by applying a transformation function to every node from bottom to top.

Declaration
public static T Rewrite<T>(this IRewriter<T> rewriter, Func<T, T> transformer, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
Func<T, T> transformer

The transformation function to apply to every node in the tree
T value

The value to rewrite
Returns
Type Description
T

The result of applying transformer to every node in the tree represented by value.
Type Parameters
Name Description
T

The rewritable tree type
Examples

Given a representation of the expression (1+2)+3,

Expr expr = new Add(
    new Add(
        new Lit(1),
        new Lit(2)
    ),
    new Lit(3)
);

Rewrite<T>(IRewriter<T>, Func<T, T>, T) replaces the leaves of the tree with the result of calling transformer, then replaces their parents with the result of calling transformer, and so on. By the end, Rewrite<T>(IRewriter<T>, Func<T, T>, T) has traversed the whole tree.

Expr expected = transformer(new Add(
    transformer(new Add(
        transformer(new Lit(1)),
        transformer(new Lit(2))
    )),
    transformer(new Lit(3))
));
Assert.Equal(expected, rewriter.Rewrite(transformer, expr));
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RewriteChildren<T>(IRewriter<T>, Func<T, T>, T)

Update the immediate children of the value by applying a transformation function to each one.

Declaration
public static T RewriteChildren<T>(this IRewriter<T> rewriter, Func<T, T> transformer, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
Func<T, T> transformer

A transformation function to apply to each of value's immediate children.
T value

The old value, whose immediate children should be transformed by transformer.
Returns
Type Description
T

A copy of value with updated children.
Type Parameters
Name Description
T

The rewritable tree type
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RewriteDescendantAt<T>(IRewriter<T>, IEnumerable<Direction>, Func<T, T>, T)

Apply a function at a particular location in value

Declaration
public static T RewriteDescendantAt<T>(this IRewriter<T> rewriter, IEnumerable<Direction> path, Func<T, T> transformer, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
IEnumerable<Direction> path

The route to take to find the descendant
Func<T, T> transformer

A function to calculate a replacement for the descendant
T value

The rewritable tree type
Returns
Type Description
T

A copy of value with the result of transformer placed at the location indicated by path
Type Parameters
Name Description
T
Exceptions
Type Condition
InvalidOperationException

Thrown if path leads off the edge of the tree
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RewriteIter<T>(IRewriter<T>, Func<T, T>, T)

Rebuild a tree by repeatedly applying a transformation function to every node in the tree, until a fixed point is reached. transformer should always eventually return its argument unchanged, or this method will loop. That is, x.RewriteIter(transformer).SelfAndDescendants().All(x => transformer(x) == x).

This is typically useful when you want to put your tree into a normal form by applying a collection of rewrite rules until none of them can fire any more.

Declaration
public static T RewriteIter<T>(this IRewriter<T> rewriter, Func<T, T> transformer, T value)
    where T : class
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
Func<T, T> transformer

A transformation function to apply to every node in value repeatedly.
T value

The value to rewrite
Returns
Type Description
T

The result of applying transformer to every node in the tree represented by value repeatedly until a fixed point is reached.
Type Parameters
Name Description
T

The rewritable tree type
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SelfAndDescendants<T>(IRewriter<T>, T)

Yields all of the nodes in the tree represented by value, starting at the top. DescendantsAndSelf<T>(IRewriter<T>, T)

Declaration
public static IEnumerable<T> SelfAndDescendants<T>(this IRewriter<T> rewriter, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
T value

The value to traverse
Returns
Type Description
IEnumerable<T>

An enumerable containing all of the nodes in the tree represented by value, starting at the top.
Type Parameters
Name Description
T

The rewritable tree type
Examples
Expr expr = new Add(
    new Add(
        new Lit(1),
        new Lit(2)
    ),
    new Lit(3)
);
Expr[] expected = new[]
    {
        expr,
        new Add(new Lit(1), new Lit(2)),
        new Lit(1),
        new Lit(2),
        new Lit(3),
    };
Assert.Equal(expected, rewriter.SelfAndDescendants(expr));
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SelfAndDescendantsBreadthFirst<T>(IRewriter<T>, T)

Yields all of the nodes in the tree represented by value in a breadth-first traversal order.

Declaration
public static IEnumerable<T> SelfAndDescendantsBreadthFirst<T>(this IRewriter<T> rewriter, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
T value

The value to traverse
Returns
Type Description
IEnumerable<T>

An enumerable containing all of the nodes in the tree represented by value in a breadth-first traversal order.
Type Parameters
Name Description
T

The rewritable tree type
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SelfAndDescendantsInContext<T>(IRewriter<T>, T)

Yields each node in the tree represented by value paired with a function to replace the node, starting at the top. This is typically useful when you need to replace nodes one at a time, such as during mutation testing.

The replacement function can be seen as the "context" of the node; calling the function with a new node "plugs the hole" in the context.

SelfAndDescendants<T>(IRewriter<T>, T) ChildrenInContext<T>(IRewriter<T>, T) DescendantsAndSelfInContext<T>(IRewriter<T>, T)
Declaration
public static IEnumerable<(T item, Func<T, T> replace)> SelfAndDescendantsInContext<T>(this IRewriter<T> rewriter, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
T value

The value to get the contexts for the descendants
Returns
Type Description
IEnumerable<ValueTuple<T, Func<T, T>>>
Type Parameters
Name Description
T
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SelfAndDescendantsInContextBreadthFirst<T>(IRewriter<T>, T)

Yields each node in the tree represented by value paired with a function to replace the node, in a breadth-first traversal order. This is typically useful when you need to replace nodes one at a time, such as during mutation testing.

The replacement function can be seen as the "context" of the node; calling the function with a new node "plugs the hole" in the context.

SelfAndDescendants<T>(IRewriter<T>, T) ChildrenInContext<T>(IRewriter<T>, T) DescendantsAndSelfInContext<T>(IRewriter<T>, T)
Declaration
public static IEnumerable<(T item, Func<T, T> replace)> SelfAndDescendantsInContextBreadthFirst<T>(this IRewriter<T> rewriter, T value)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
T value

The value to get the contexts for the descendants
Returns
Type Description
IEnumerable<ValueTuple<T, Func<T, T>>>
Type Parameters
Name Description
T
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ZipFold<T, U>(IRewriter<T>, Func<T[], IEnumerable<U>, U>, T[])

Flatten all of the nodes in the trees represented by values into a single value at the same time, using an aggregation function to combine nodes with the results of aggregating their children. The trees are iterated in lock-step, much like an n-ary Zip<TFirst,TSecond,TResult>(IEnumerable<TFirst>, IEnumerable<TSecond>, Func<TFirst,TSecond,TResult>).

When trees are not the same size, the larger ones are truncated both horizontally and vertically. That is, if a pair of nodes have a different number of children, the rightmost children of the larger of the two nodes are discarded.

Declaration
public static U ZipFold<T, U>(this IRewriter<T> rewriter, Func<T[], IEnumerable<U>, U> func, params T[] values)
Parameters
Type Name Description
IRewriter<T> rewriter

The rewriter
Func<T[], IEnumerable<U>, U> func

The aggregation function
T[] values

The trees to fold
Returns
Type Description
U

The result of aggregating the two trees
Type Parameters
Name Description
T

The rewritable tree type
U

The return type of the aggregation
Examples

Here's an example of using ZipFold<T, U>(IRewriter<T>, Func<T[], IEnumerable<U>, U>, T[]) to test if two trees are syntactically equal.

static bool Equals(this Expr left, Expr right)
    => left.ZipFold<Expr, bool>(
        right,
        (xs, results) =>
        {
            switch (xs[0])
            {
                case Add a1 when xs[1] is Add a2:
                    return results.All(x => x);
                case Lit l1 when xs[1] is Lit l2:
                    return l1.Value == l2.Value;
                default:
                    return false;
            }
        }
    );